1. Field of the Invention
The present invention relates to a method of entering a digitized audio signal into a data processing apparatus, such as a personal computer, method of transmitting the audio signal, and audio signal transmitting apparatus and audio signal receiving and reproducing apparatus which permit transmission of the audio signal according to this signal transmitting method.
2. Prior Art
When a computer receives stereo audio signals, analog signals may be input via analog input terminals, and converted into PCM (Pulse Code Modulation) data in the inside of the computer, or digital audio signals may be input via serial ports, such as RS-232C, or SCSI (Small Computer System Interface) ports, for example. In the former method, however, the input signals in the analog format are likely to be affected by noise from the computer. The latter method has a problem of a slow input speed, and, in most cases, cannot be used for exclusively inputting audio signals.
In view of the above situation, an audio input interface has been developed which is designed to convert digitized audio signals into serial data, and transmit the serial data via an exclusive digital audio input terminal, such as SPDIF, as shown in FIG. 1.
In the conventional audio interface as shown in FIG. 1, analog audio signals SL, SR of left (L) and right (R) channels are converted into digital signals by respective A/D converters 101, 102, and packeted by a packet circuit 103 to be converted into serial data, which is then transmitted to a personal computer 200. On the side of the personal computer 200, the received serial data are synchronized by a PLL (phase-locked loop) circuit, and the resultant packet data is decoded by a decoding circuit 202 and reassembled into original digital data. Thus, the circuit arrangement tends to be complicated, with a result of an increased cost.
The other method of transmitting digitized audio signals may be roughly classified into a method of transmitting the input signals after converting them into analog signals, and a method of transmitting the digital signals as they are. FIG. 2 shows an example of the former method. In this example, digital audio signals of L channel and R channel which are reproduced in a reproducing system (not shown) are converted into corresponding analog audio signals by respective D/A converters 301L and 301R, and then amplified by respective amplifiers 302L and 302R. The analog audio signals of the two channels obtained from the amplifiers 302L and 302R are then transmitted over respective cables 303L and 303R, amplified by amplifiers 304L and 304R, and then generated from speakers 305L and 305R.
FIG. 3 shows one example of the method of transmitting audio signals in the form of digital signals. In the example of FIG. 3, a packet of digital audio signals of L channel and R channel is transmitted from a digital output circuit 401. This packet is transmitted to a demodulator circuit 403 over a cable 402, and is demodulated by this demodulator circuit 403 into the original digital audio signals of the L channel and R channel. These digital audio signals of the respective channels are converted into analog audio signals by D/A converters 404L and 404R, amplified by amplifiers 405L, 405R, and then generated from speakers 406L and 406 R.
The above-described prior art method of FIG. 2, in which the audio signals are transmitted as analog signals, suffers from deterioration of the quality of sound reproduced from the speakers if noise is superposed on the analog signals during their transmission. Where this method is employed within digital equipment, such as a personal computer, in particular, noise involved in the digital signal system is likely to be superposed on analog audio signals during their transmission, whereby the quality of reproduced sound is considerably deteriorated. On the other hand, the method of FIG. 3 is advantageous in that the transmitted audio signal, which is a digital, signal, is highly resistant to noise. To implement this method, however, there is a need to provide the digital output circuit for assembling and transmitting a packet of digital audio signals, and the demodulator circuit for demodulating this packet, which may increase the size and cost of the whole apparatus.
It is therefore a first object of the present invention to provide a method of entering an audio signal, which method enables a simple circuit to use input terminals of analog audio signals to enter a digital audio signal into a data processing apparatus, and wherein a transmitted signal is unlikely to be affected by noise even in an environment having a lot of noise.
It is the second object of the invention to provide an audio signal transmitting method that permits an audio signal to be transmitted assuring high resistance to noise, without significantly changing the construction of the known apparatus, and to provide an audio signal transmitting apparatus and an audio signal receiving and reproducing apparatus for transmitting the audio signal according to this method.
To attain the first object, the present invention provides a method of entering an audio signal into a data processing apparatus, wherein analog audio signals of at least two channels as the audio signal are digitized by and transmitted from an audio signal output device on a side of an audio source to an audio signal input device on a side of the data processing apparatus, comprising the steps of a) supplying a clock signal from the audio signal input device to the audio signal output device; b) performing delta-sigma (xcex94xcexa3) modulation on the analog audio signals of at least two channels in the audio signal output device so as to convert each of the analog audio signals of at least two channels into one-bit digital audio data for each of the at least two channels, based on the clock signal supplied to the audio signal output device, c) alternately selecting the one-bit digital audio data for the each channel, based on the clock signal, in the audio signal output device, to perform time-division multiplexing on the one-bit digital audio data for the at least two channels, to thereby produce one-bit multiplex audio data, and d) supplying the one-bit multiplex audio data from the audio signal output device to the audio signal input device.
Preferably, the multiplex audio data and the clock signal are respectively transmitted to the audio signal input device and the audio signal output device, through respective input lines provided in the data processing apparatus for receiving analog audio stereo signals.
Further preferably, the method of entering an audio signal further comprises the step of separating the one-bit multiplex audio data into at least two streams of data corresponding to respective ones of the at least two channels and converting each of the at least two streams of data into multiple-bit PCM data for the each channel in the audio signal input device.
To attain the first object, the present invention also provides a data processing apparatus having an interface comprising a) a block which generates a clock signal to an external device, b) a block which receives multiplex audio data produced by one-bit quantization of audio data of at least two channels in synchronization with the clock signal and time-division multiplexing of the quantized audio data based on the clock signal in the external device, and c) a block which processes the received multiplex audio data in synchronization with the clock signal.
To attain the second object, the present invention provides a method of transmitting an audio signal from an audio signal transmitting apparatus to an audio signal receiving apparatus, comprising the steps of a) performing delta-sigma (xcex94xcexa3) modulation modulation and time-division multiplexing on digital audio signals of at least left channel and right channel as the audio signal in the audio signal transmitting apparatus, to produce bit stream data as a result of the time-division multiplexing of the digital audio signals, b) transmitting the bit stream data and a clock signal that is in synchronization with the bit stream data, from the audio signal transmitting apparatus to the audio signal receiving apparatus, and c) separating the bit stream data into at least two streams of data corresponding to respective ones of the at least left channel and right channel, based on the clock signal, in the audio signal receiving apparatus.
To attain the second object, the present invention also provides an audio signal transmitting apparatus comprising a one-bit D/A converter that performs delta-sigma (xcex94xcexa3) modulation and time-division multiplexing on digital audio signals of at least left channel and right channel, to produce time division multiplexed bit stream data, a separator that separates the bit stream data into at least two streams of data corresponding to respective ones of the at least left channel and right channel, based on a clock signal that is in synchronization with the bit stream data, an analog signal reproducing device which converts the bit stream data of each of the at least left channel and right channel, into a corresponding analog signal, a plurality of signal output terminals that respectively correspond to the at least left channel and right channel, and a selecting device which selects one of first and second modes, the first mode being established by supplying the bit stream data and the clock signal to respective ones of the signal output terminals corresponding to the at least left channel and right channel, the second mode being established by supplying the analog signal of each of the at least left channel and right channel which is transmitted from the analog reproducing device, to one of the signal output terminals which corresponds to the each channel.
To attain the second object, the present invention further provides an audio signal receiving and reproducing apparatus comprising a plurality of signal input terminals that respectively correspond to at least left channel and right channel, a plurality of analog signal reproducing devices that respectively correspond to the at least left channel and right channel, a separator that separates time division multiplexed bit stream data, into at least two streams of data corresponding to respective ones of the at least left channel and right channel, in synchronization with a clock signal, and a selecting device that selects one of first and second modes, the first mode being established by transmitting input signals received by the signal input terminals corresponding to the at least left channel and right channel to the separator, the input signals being the bit stream data and the clock signal, and transmitting the at least two streams of data corresponding to the respective ones of the at least left channel and right channel, from the separator to the analog signal reproducing devices corresponding to the respective channels, the second mode being established by transmitting input signals received by the signal input terminals corresponding to the at least left and right channels, to the analog signal reproducing devices corresponding to the respective channels.